Gergis’ Two Medieval Proxies

IPCC AR5 (First Draft) cited Gergis et al as follows:

New paleo records from Australasia provide evidence of MCA warming around 1250–1330 CE, [my bold] somewhat later than maximum medieval warmth described from many Northern Hemisphere regions (Gergis et al., submitted). Following peak medieval warmth in the early 1300s, a cooling trend reaching a temperature anomaly of approximately 0.5 ± 0.18°C below the 1961–1990 CE climatology during the peak of the LIA, 1830–1859 CE (Gergis et al., submitted).

In addition, the Gergis reconstruction was one of a number of regional reconstructions compared to model simulations.

The “New” Paleo Records
What are the “new paleo records from Australasia” that shed this new light on the medieval period?

Gergis et al has only two proxies in the period 1250-1318: tree ring series from Tasmania and Oroko Swamp, NZ, both from Ed Cook. Neither of them are “new’. Nor is a third long proxy, Law Dome O18 (screened out by Gergis.)

The “New” Gergis Proxies in IPCC AR4
Not only are the “new” Gergis proxies not new; they were prominently displayed in the AR4 section on SH proxies. Indeed they are the only two long proxies so displayed. The commentary in AR4 is as follows:

The paucity of SH proxy data also means that uncertainties associated with hemispheric temperature estimates are much greater than for the NH, and it is more appropriate at this time to consider the evidence in terms of limited regional indicators of temperature change (Figure 6.12).

The long-term oscillations in warm-season temperatures shown in a tree ring reconstruction for Tasmania (Cook et al., 2000) suggest that the last 30 years was the warmest multidecadal period in the last 1 kyr, but only by a marginal degree. Conditions were generally warm over a longer period from 1300 to 1500 (Figure 6.12). Another tree ring reconstruction, of austral summer temperatures based on data from South Island, New Zealand, spans the past 1.1 kyr and is the longest yet produced for the region (Cook et al., 2002a).

The two long series illustrated in AR4 come from the same two sites as the two long Gergis series.

In fact, the Gergis version of Cook’s Tasmania series appears to be identical to the version used by IPCC, as shown in the panel below, where the Gergis versions is overprinted onto the IPCC graphic (rescaling by eye). It appears that Gergis used a newer and somewhat different version of Cook’s Oroko Swamp series, but the differences are not material other than Gergis has values post-1957, while AR4 didn’t. The original article says that logging impacted post-1957 growth; Gergis says that her post-1957 have been adjusted for post-1957 logging (citing a pers comm from Cook), but the adjustment itself is not shown or discussed in the referenced artice.)
Figure 3. IPCC Figure with Gergis series overprinted (rescaled by eye). Top – Tasmania: Gergis overlay in cyan is indistinguishable; bottom Oroko NZ – overlay in red.

Thus, the statement in AR5 that the Gergis results for the medieval period come from “new paleo records” is untrue. I wonder if reviewers picked this up.

Mann and Jones 2003

IPCC AR4 referred to Mann and Jones 2003, which included a SH reconstruction, as a primary SH reference, noting that they used “only three series”.

There are markedly fewer well-dated proxy records for the SH compared to the NH (Figure 6.11), and consequently little evidence of how large-scale average surface temperatures have changed over the past few thousand years. Mann and Jones (2003) used only three series to represent annual mean SH temperature change over the last 1.5 kyr.

Remarkably, and I hadn’t noticed this until just now, IPCC AR4 didn’t show the Mann and Jones SH reconstruction, for reasons that will become clear below.

Mann and Jones 2003 also screened SH proxies, but with interestingly different results than Gergis. They started with 5 long proxies: Tasmania tree rings, Oroko, Law Dome plus two South American proxies – Quelccaya O18 and a Chilean tree ring series. Whereas Gergis rejected Law Dome and kept Oroko, the screening procedure of Mann and Jones did the opposite: it rejected Oroko and kept Law Dome. Their screening was based on decadal correlation to local instrumental temperature. They reported that Law Dome had a (decadal) correlation of 0.76 to instrumental temperature, while Oroko had negative correlation (-0.25). These results were plotted on Figure 1 of Mann and Jones 2003, shown below;

Reconstructions – Law Dome vs Oroko
Using Law Dome O18 rather than Oroko led Mann and Jones to SH temperature reconstruction that didn’t have a Hockey Stick, as shown in the excerpt from Mann and Jones 2003 shown below.

This reconstruction wasn’t illustrated in AR4. Instead, IPCC commented on the reconstruction as follows:

The recent proxy-based temperature estimates, up to the end of the reconstruction in 1980, do not capture the full magnitude of the warming seen in the instrumental temperature record. Earlier periods, around AD 700 and 1000, are reconstructed as warmer than the estimated level in the 20th century, and may have been as warm as the measured values in the last 20 years.

Now compare the Mann and Jones reconstruction with the Gergis reconstruction which is shown in AR5 (First Draft) as part of its panel graphic comparing regional reconstructions to models, as shown below. Both have rather small amplitudes; however, the Gergis reconstruction has a small Hockey Stick.

Law Dome
Much of the difference between the Mann and Jones 2003 and the Gergis reconstruction arises merely from the presence/absence of the Law Dome O18 series, as can be seen by comparing the Law Dome O18 series (shown below) with the Mann and Jones 2003 SH reconstruction.

Figure . Law Dome O18 record. Plotted from LD2.1yyr data set sent by email by Tas van Ommen on 2006-03-14.

If you compare the Law Dome series shown here with the Mann and Jones 2003 SH reconstruction, you can see how the Law Dome series directly affects its results. And thus why screening Law Dome out and replacing it with Oroko leads to a very different result. Although Gergis carried out an elaborate ensemble of 3000 permutations, none of these permutations included Law Dome.

In passing, I’ll remind readers of my efforts as an IPCC AR4 reviewer to get the IPCC authors to show the Law Dome data (which I’d received in March 2006 just before review comments) – see CA post here.

CRU’s Tim Osborn led the movement against showing the data. He wrote (709. 1153233036.txt) presenting the problem:

(1) Jones/Mann showed (and Mann/Jones used in their reconstruction) an isotope record from Law Dome that is probably O18 (they say “oxygen isotopes”). This has a “cold” present-day and “warm” MWP (indeed relatively “warm” throughout the 1000-1750 period). The review comments from sceptics wanted us to show this for obvious reasons.

Osborn and the IPCC authors wanted not to show it also apparently “for obvious reasons”, a picture being worth a thousand words.

Law Dome also plays an interesting role in Mann et al 2008 – one that I hadnt appreciated before, but will re-visit. Mann et al 2008 used Law Dome O18, but did not use the long Law Dome O18 series that he had used in Mann and Jones 2003 (with its inconvenient MWP) – which would have had an impact on the sparse SH network. Instead Mann’s version of Law Dome O18 went only from 1761-1970 (!) It is a truncation of an obsolete version. I’ll discuss this backstory in another post as well.

The above graphic shows a 2003 version of Law Dome O18 (which Tas van Ommen sent me in 2006.) Despite the overwhelming importance of O18 as a paleoclimate proxy and the importance of Law Dome as a high-accumulation (high-resolution) core, the Law Dome O18 record shown here has never been archived (or even published by the authors.) The authors have been unfortunately diverted by other projects. [Note: June 4 – the Law Dome 2.1kyr O18 series does not turn up on a search of the Australian Antarctic Data Center under “law dome”. However, the existence of the series is reported at the NASA Global Change Directory, which contains a link to a webpage
which states “The file you have tried to download is not yet available for public access. Contact the Australian Antarctic Data Centre, using the request form, for further details.” Van Ommen says by email that he has not received requests for the data, but will reconsider the matter.]

I will discuss the puzzling history of this important proxy in a follow-up post.

45 Comments

Wow, this is remarkable. I can understand there is a lack of medieval era proxies for the SH, but how can anyone think it is possible to say anything reliable about the MWP or lack thereof when the SH is such a blank slate for the medieval period?? And why do climatologists seem to go to such lengths to obscure how little is known about temps in the SH during the medieval period??

They justify (to themselves) not showing Law Dome on the grounds that its being affected by something other than temperature (“regional variations”). This may well be true.

But how do they then know that O18 records going the “right” way are not also being affected by “regional variations”. The Dasuopu O18 series, with a big HS, is clearly affected by “regional variations” as its O18 increase is implausible as temperature. But Thompson includes it in his composite anyway.

looking at your Law Dome O18 plot it seems that it is suffering with the same (but earlier) problem as tree rings – a decline in the latter years.

Why do you suggest that the tree ring data is of no use predicting temperature because of the decline and should never be included in reconstructions. But the DO18 plot you give should have been included in the document under discussion.

Looking at bore hole temperature (measured) from Law dome the profile is nothing like that you plot. Does this not suggest that D018 or borehole temperatures are at fault? But D018 does not match with current temperatures, and bore hole temperature do.

Borehole temperature reconstructions require the inversion of near singular matrices. i would place little weight on them.

The Law Dome dO18 goes down – this requires an explanation. There is a monotonic physical relationship between temperature and isotope fractionation, whereas tree rings are non-monotonic (upside down quadratic) = an entirely different hornet’s nest.

In an article on Law Dome in the 1980s, Morgan, as I recall, observed that there had been a very long term decline in Law Dome O18 and that some part of this might be due to increasing elevation.

So Rattus are you saying that if the proxies “go the wrong way” every possible effort should be made to find any possible (trivial) reason to exclude them?
However if they “go the right way”, then they are obviously important indicators of past climatic change and must be included without the bother of doing any of the backgound digging that was applied to the “wrong ones”?

“I will discuss the puzzling history of this important proxy in a follow-up post.”

My previous understanding was that tree ring width was mostly connected to ground moisture availability, but there was speculation, extant before the CO2 scare, that certain tree-line species’ growth may be more modulated by severe cold and length of cold season. That’s why the dendros go to the bristlecones and Siberian trees for temperature info. So where is the science that tree rings in Tasmania and New Zealand show much about anything about temperatures?

Tasmania has been extensively logged for nearly two centuries for wood to build wooden clipper ships. Wooden Boat magazine had a great article on it several years ago, will have to check my old magazine pile to find the article. As far as New Zealand, the Maoris
are great sea-going people, experts in falling large trees to make dug out canoes, or
making catamarans. Both of those areas would have extensive utilization of woodlands going back to at least 1000 AD for New Zealand, and much further for Tasmania.

It’s still early days, but 3 matters concern me.
1. Gergis et al in a paper about Australasia, appear to use no proxies from mainland Australia, which is that large land area with over 1,000 temperature recording stations and about that many climate scientists. I wonder why?
2. Argo data shows an SST plateau band with latitude; near the tropics, 31 deg C is seldom exceeded. See Willis Eschenbach at http://wattsupwiththat.com/2012/02/09/jason-and-the-argo-notes/ then a copy of one of his figures that I’ve slipped onto my website for the moment:http://www.geoffstuff.com/argo-surface-temperatures-by-latitude%5b1%5d.jpg If the temperatures around the Equator do not change so much, this must lead to less information in coral proxies.
3. See Climategate for the Huon pine seies of Ed Cook, quoted as
“In my conversations with Brendan, it has occurred to
me that something analogous to what you find in your data (a systematic
departure between tree rings and temperature over the past few decades)
also is apparent in some of the Huon pine data. Specifically, the BCH
site of Brendan’s, which is the second highest site compared to Lake
Johnston, shows the same effect as you see, at least in the ring widths
anyway. We don’t yet have density data for that site. The high-pass
variations in ring width lock in beautifully with temperature, better in
fact than does Lake Johnston. However, the low-pass side goes down over
the past 30 years years as temperatures have increased. Brendan and I
have speculated about this a lot. My pet theory is that temperatures
have risen sufficiently to cause net photosynthesis to go into deficit
occasionally (i.e. respiration exceeds primary photosynthesis).”

“We don’t yet have density data for that site. The high-pass
variations in ring width lock in beautifully with temperature, better in
fact than does Lake Johnston. However, the low-pass side goes down over
the past 30 years years as temperatures have increased. Brendan and I
have speculated about this a lot.”

Geoff thanks for the excerpt. Perhaps we can get Jim Bouldin to comment on it with regards to pre-selecting valid proxy thermometers.

Of interest NIWA has recently revised the Hokitika temperature series that was used for calibration in the Cook study http://www.niwa.co.nz/sites/default/files/import/attachments/Hokitika_CompositeTemperatureSeries_15Dec2010_FINAL.pdf, and makes the observation “Because of lower confidence in early temperature measurements the revised temperature series is not constructed prior to 1900” although Cook uses the 1866 -1880 period to verify their models. Whether any of this adjustment would make any difference to Cook’s results isn’t clear (it would however most certainly change the relationship between the post 1957 actual data added to the series and the balance of it).

The evidence are tree trunks a few meter long, which need a warmer climate than present to grow on those sites.

Another older paper shows evidence of the MWP in New Zealand from glacier records, but it is less clear:
Glacial geological evidence for the medieval warm period Jean M. Grove and Roy Switsur CLIMATIC CHANGE
Volume 26, Numbers 2-3 (1994), 143-169, DOI: 10.1007/BF01092411

Jorge Montt glacier is a calving glacier, and those tree stumps were found near sea level, local treeline is higher when the terrain is ice free.

The warmer/colder climate is a limiting factor, not for tree growth in this case, but for the presence of the overriding glacier ice.

If it were a surging glacier it would mean that average ELA was much higher, and therefore warmer.

I am not aware of a significant reduction in precipitation in the last 1000 years in Patagonia, which would certainly cause a smaller glacier. I think we are pretty safe if we correlate precipitation with solar radiation, which in any case is not a limiting factor for trees in the region at present. If I remember correctly, treeline further south, in Torres de Paine, is about 900 m.

dO18 can correlate with temperature, for well-established physical reasons, but sometimes it is picking up variations in the seasonality of precipitation rather than annual average temperature, and sometimes just wind direction, since distance from the ocean affects atmospheric d18O. So it can be useful, but is hardly “accurate”.

Tree rings, on the other hand, probably have a quadratic relation to temperature, as has been argued by Craig Loehle. If the relationship were monotonic, the bristlecone pines in the Amazon would be the size of giant redwoods, but in fact that climate is too hot for them to thrive. And then trees also respond strongly to precipitation, as well as to fertilization by volcanic dust, agricultural dust, and even CO2. This makes them extremely questionable as temperature proxies.

Gergis et al do in fact use a third medieval proxy, the Palmyra coral series, which begins in 1149. However, according to their Figure 1, it drops out around 1225, and then reemerges circa 1310 (only to disappear again circa 1450). From Steve’s post, I gather the exact date of its reappearance is 1318.

When only three persistent series are being averaged together, the sudden disappearance or reappearance of one of them can cause a big shift in the average. The reappearance of Palmyra c 1318 may help account for the sudden spike in the 30-year smoothed Gergis series c 1330. Its disappearance circa 1225 may also have something to do with the decline after 1250.

This patching together of different periods with different proxies really worries me. Especially at the join points. I can imagine the early period in this case with 2 series ending at one temperature and the following section with lots of series beginning at a radically different temperature. The basis for joining these up escapes me. It just seems like a bodge to try to use all your data without ever being proven or justified.

the Law Dome 2.1kyr O18 series does not turn up on a search of the Australian Antarctic Data Center under “law dome”. However, the existence of the series is reported at the NASA Global Change Directory, which contains a link to a webpage
which states “The file you have tried to download is not yet available for public access. Contact the Australian Antarctic Data Centre, using the request form, for further details.” Van Ommen says by email that he has not received requests for the data, but will reconsider the matter.

Re: Hu McCulloch (Jun 4 08:00),
I’ve been planning to do a post on the medieval coral in Kim Cobb’s Palmyra series. A theory of a “cool” medieval Pacific has been more or less constructed on this single coral, which can fairly be called the “most influential coral in the world”. (Stay thirsty, my friends.)

I’ve actually heard this from some others in the Paleo community – about how reliant *some* reconstructions are on a single coral in the pacific for these prominent “La Nina” conditions. That being said there’s a 1000+ year recon of ENSO that appears to have La Nina conditions in the pacific as well (published last year? or the year before).

Why does it disappear from Gergis’s Figure 1 circa 1225-1310, and again circa 1450-1620? Are these holes in the original series?

Although Gergis doesn’t use the Outlaw Dome, she does use Vostok, but only after 1774 even though it goes back 100Ks of years. How much annual resolution is really there after 1774, and is pre-1774 any worse?

Steve: The Palmyra series is not continuous. They dated the coral by Uranium-Thorium. Accumulation at Vostok (and thus resoltuion) is about 10% of the corresponding accumulation at Law Dome. Law Dome is probably the highest resolution ice core in the world – and by a considerable margin.

Oroko is like a shiny coin, a rare long SH reconstruction, unfortunately tainted by MWP and LIA(3759, Cook to Briffa, 30 Aug 2000):

“Here is the Oroko Swamp RCS chronology plot in an attached Word 98 file and actual data values below. It certainly looks pretty spooky to me with strong “Medieval Warm Period” and “Little Ice Age” signals in it. It’s based on substantially more replication than the series in the paper you have to review (hint, hint!). In terms of rbar, sample size, and eps, it is probably okay back to about AD 980 at this time. I still have 3-4 more subfossil sections to process, but it is doubtful that the story will
change much.”

Cook was wrong, the story is still changing. The original data apparently ended in 1957 and had instrument data tacked on. Maybe Gergis can call it a “new” reconstruction by adding in the post-1957 data and taking a SWAG at an adjustment for logging impacts.

From Cook 2002, GRL 29, the reason for stopping the NZ Oroko Swamp record at 1958 was disturbance from later logging. However, over the Tasman, Cook knew in 1997 that the ‘divergence’ problem existed in Tasmania’s Huon Pines, where the low frequency signal drifted off its hoped-for course. It is possible by association that the divergence problem and not logging was the cause of the hiatus, in which case some evidence would be needed from Gergis et al 2012 as to how to differentiate the possible causes when they extend data beyond 1958 with undescribed new techniques.
The 2002 Oroko swamp effort was partially compromised by a lack of instrumental readings during part of the calibration/verification period 1881-1893, so nearby sea temperatures were used instead. Next, there is present doubt about Salinger’s construction of the historic thermometer record for Hokitika, the main reference station. Finally, if it is admissible to use sea temperatures as a calibration, surely for closing the loop, there should be a complete calibration using sea temperature rather than land temperature, up to the present.
Finally, in the context of selective sampling, one is left wondering what was meant by Cook 2002 “New Zealand, with its large expanses of intact forest that support several tree species with known
dendroclimatic potential.” Just what is dendroclimatic potential, in detail, and how is it known ahead of experiments?
Really, when you look at it, there are several worrying aspects to this reconstruction which, if not addressed in the yet-to-be released data of Gergis et al 2012, ought to be.

“Their screening was based on decadal correlation to local instrumental temperature. They reported that Law Dome had a (decadal) correlation of 0.76 to instrumental temperature, while Oroko had negative correlation (-0.25).”

The selection criteria in Gergis is a correlation of proxy to instrumental temperature with a probability =<0.05. It says nothing about negative or positive coefficients.

The Maori arrived in New Zealand during the Medieval warm period and, if two-way voyaging took place, it was not for very long. My friend Dr Philip Houghton, in his scholarly book “People of the Great Ocean”, speculated that the Maoris arrived “during a particularly favourable period of summer weather”. I conclude that the presence of the Maoris in New Zealand is evidence that the Medieval warm period included New Zealand. Quite clearly, it was characterised by the good weather needed for ocean voyaging in an open canoe.

Regarding Easter Island, there is evidence that, at some stage, Pitcairn Island was used as a way station for two-way voyaging. It seems that this ended a considerable time before Fletcher Christian and his crew arrived there about 1780.

temperature reconstruction for the combined land and oceanic region of Australasia (0°S-50°S, 110°E-180°E).

The study lists Palmyra Atoll as being at 6° S, 162° E, so within the study area. Wikipedia has the location at 5°52′ N, 162°06′ W, or over 2100Km (1300 miles) outside the study area. On a similar basis, Rarotunga in the Cook Islands (for which there are two separate coral proxy studies), is listed as being at 21° S, 160° E. Again well within the study area. Wikipedia has the location as 21° 14′ 0″ S, 159° 47′ 0″ W, or about 2000Km (1250 miles) outside the study area. The error has occurred due to a table with columns headed “Lon (°E)”, and “Lat (°S). Along with the two ice core studies from Vostok Station, Antarctica (Over 3100km, 1900 miles south of 50° S) there are 5 of the 27 proxies that are significantly outside the region.

Yes, you notice the wrong coords when you go looking for factors like distance. It’s traditional to put latitude before longitude (contra Gergis table 1). For finding the study area to seek weather stations it would be useful to express degrees of lat and long to about 4 places after the decimal.
There are also problems with assertions like “if the Indo Pacific Warm Pool was indeed the origin of the relative warmth associated with the MCA,” because one is led to ask the origin of the warmth of the Indo Pacific Warm Pool. Going around in circles?
I’m working from a pre-release version of the paper, so apologies if the above are corrected in the final.

What I found interesting was that it took until the 2000s to get a long tree-ring
series for New Zealand. And that they argue to an actual Medieval Warm Period in
at least some part of the Southern Hemisphere, partially debunking the claim that
the MWP is mainly a Northern Hemisphere artifact, or merely local.

[…] However, hockey stick sleuth and statistics ace Steve McIntyre (prompted by a tip from Jean S) could not resist the temptation of taking a good look at the curve. Here he found unexpected things (see his report at Climate Audit). […]